Method and associated apparatus for increment accuracy of geographical foreign agent topology relation in heterogeneous access networks

ABSTRACT

One aspect of the present invention regards a method of coordinating the handoff of a mobile carrier between a first access network and a second access network, the method including handing off from a first access network that the mobile carrier is currently operating within to a second access network and building a physical access network topology based on the handing off without input from either the first access network or the second access network.

[0001] Applicants claim, under 35 U.S.C. § 119(e), the benefit ofpriority of the filing date of Apr. 5, 2002, of U.S. Provisional PatentApplication Serial No. 60/370,302 filed on the aforementioned date, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to the field of wireless networks.

[0004] 2. Discussion of Related Art

[0005] It is well known that a number of networks and service providerscan exist simultaneously within a particular geographical area. Withthis environment in mind, establishment of communication between amobile device within the geographical area and another communicationdevice often involves the handoff of the signal from one network toanother network as the person operating the mobile device moves withinthe geographical area. Since there often are many variations in accessnetworks, service providers and mobile devices, it is very difficult toassure seamless communication within the geographical area for a varietyof mobile devices.

[0006] One proposal at establishing seamless communication for mobileusers as well as application service providers is to use a HyperOperator Overlay architecture, such as described in F. Watanabe, J. Cao,S. Kurakake, “Geographical access network topology estimation inheterogeneous access networks,” IEEE VTC'02 paper no. 775.

[0007] An example of a known Hyper Operator Overlay network architectureis schematically shown in FIG. 1. The Hyper Operator Overlay (HOO)network architecture 100 combines different access networks to providethe most suitable access network to each available service. The HOOnetwork 100 includes different access networks 102A-D, service/contentproviders 104A-B and a hyper operator 106 located in the Internet. Nodes112A-D of the access networks 102A-D are in communication with HyperOperator Overlay nodes 114A-B of the Internet which are in turn incommunication with a Hyper Operator Overlay node 14C Thus, nodes 112A-Dare in communication with Hyper Operator Overlay node 114C. The hyperoperator 106 communicates with the Hyper Operator Overlay nodes 114A-C,access networks 102A-D, service providers 104A-B and company intranet108 and works to coordinate different access networks and serviceproviders 104A-B (such as, yahoo.com) including private intranets (e.g.company intranet 108) in order to have seamless communications.

[0008] The mobile device, such as a cell phone, PDA or a lap topcomputer 110, supports different access network technologies such asWLAN, mobile phone, Bluetooth, ADSL, etc. Instead of having severalservice agreements with different access networks 102 and serviceproviders 104, a user using the mobile device will only need to have asingle service agreement with the hyper operator 106. Because of aservice contract with the hyper operator 106, the user can gain accessto different access networks 102 by the mobile device withoutestablishing new service contracts.

[0009] The HOO network 100 does not require modifications to existingaccess networks. The HOO network 100 can work as a broker or a bridgebetween different access networks and service providers, and cancoordinate service offered by different access networks and serviceproviders. As described in S. Weinstein, “The mobile internet: wirelessLAN vs. 3G cellular mobile,” IEEE Commun. Mag., vol.40 no.2, pp.26-28,Feb. 2002, the HOO network 100 has three features of interest:

[0010] 1) For end users who are already subscribers of major serviceproviders, transparent Internet access is provided in many localenvironments without having to subscribe with each Palm LAN operator

[0011] 2) For major service providers, extension of services offered totheir subscribers without having to invest in additional accessinfrastructure; and

[0012] 3) For public access wireless LAN operators, a vast potentialuser population acquired without having to sign up individual customers.

[0013] In the hierarchical coverage area of the HOO network 100, theremay be a variety of sizes of access networks, as described in E.A.Brewer et al., “A network architecture for heterogeneous mobilecomputing,” IEEE Pers. Commun., vol.5, no.5, pp.8-24, Oct. 1998 and M.Stemm and R. H. Katz, “Vertical handoffs in wireless overlay networks,”Mobile Networks and Applications, vol.3, no.3, pp.335-350, 1998. Anaccess network with small coverage area has a relatively high-bandwidth,while an access network with large coverage area has a relatively smallbandwidth. The vertical handoff between different access networks can beclassified into two categories: an upward vertical handoff is a handoffto a wireless overlay with a larger cell size (and lower-bandwidth) anda downward vertical handoff is a handoff to a wireless overlay with asmaller cell size (and higher bandwidth). It is well known that theupward vertical handoff has a time critical issue of handoff processingtime when the mobile device moves out from the access network with asmaller cell to that with a larger cell. Also, a quick authenticationand QoS adjustment are required, especially for real time applicationssuch as video and voice, because different access networks possessinherent diversity in terms of operating frequencies, access schemes,QoS supports, monetary costs, and traffic conditions.

[0014] However, current independent management for user, mobility,resource allocation, authentication/authorization, security at eachaccess network makes it difficult to coordinate heterogeneity and tomaintain connectivity. In addition, minimizing modification of thecurrent access network would be preferable. A couple of schemes tocoordinate network heterogeneity and to maintain connectivity have beenconsidered. One approach proposes a common core network to coordinatevarious access networks as described in G. Wu, “MIRAI architecture forheterogeneous network,” IEEE Commun. Mag., vol.40, no.2, pp.126-134,Feb. 2002. This approach attempts to construct the common core networkbetween the Internet and access networks to handle heterogeneity ofdifferent access networks. It requires additional modification toconverge different network cores whose functions are mobilitymanagement, authentication/authorization, paging etc. Therefore,existing access network operators may not be able to join the new commoncore network architecture easily. In addition, the infrastructureinstallation cost is expected to increase. Also, the common core networkdoes not absorb heterogeneity of higher layer requirements.

[0015] Another approach for coordinating heterogeneity and maintainingconnectivity is to use the cooperative and enhanced hybrid networks(DRiVE project) which interface directly with access networks and theInternet as described in R. Walsh, L. Xu, T. Paila, “Hybrid networks—asstep beyond 3G,” WPMC'00 pp.109-114, Bangkok, Nov. 2000.

[0016] In order to realize both of the above described approaches formitigating heterogeneity, the new core, which integrates an independentmanagement owned by each access network, has to be developed andinstalled. Furthermore, the need for a standardization effort andbusiness commitment is inevitable.

[0017] The geographical access network configuration (e.g., location ofbase station, coverage area, capacity etc) is assumed to be known to theoperator because the operator owns its access network. However, theHyper Operator will not own the access network. It only owns users.Whenever the user uses an access network, the access network operatorwill charge to the Hyper Operator. In this model, the Hyper Operator maynot be able to get geographical access network information easily. Evenif the Hyper Operator can get this information, the geographicalcoverage area, especially WLAN and WPAN (wireless personal area network,like Bluetooth), is dynamically changed. Therefore, the latestgeographical access network information is not available in the HyperOperator.

SUMMARY OF THE INVENTION

[0018] One aspect of the present invention regards a method ofcoordinating the handoff of a mobile carrier between a first accessnetwork and a second access network, the method including handing offfrom a first access network that the mobile carrier is currentlyoperating within to a second access network and building a physicalaccess network topology based on the handing off without input fromeither the first access network or the second access network.

[0019] A second aspect of the present invention regards a method ofdetermining a geographical relationship between a first access networkand a second access network as a mobile device moves between a firstaccess network and a second access network. The method includes losingconnection with a mobile device located within a first access network,establishing connection with the mobile device within a second accessnetwork and determining a geographical relationship between the firstaccess network and the second access network based on a chronologicalrelationship between a time of the losing connection and a time of theestablishing connection.

[0020] Each of the above aspects of the present invention provides theadvantage of coordinating heterogeneity and maintaining connectivity fornetworks.

[0021] Each of the above aspects of the present invention provides theadvantage of increasing the accuracy of a geographical access networkconfiguration.

[0022] Each of the above aspects of the present invention provides theadvantage of estimating a geographical access network configuration eventhough no operational information is provided from each access network.

[0023] The present invention, together with attendant objects andadvantages, will be best understood with reference to the detaileddescription below in connection with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 schematically illustrates a known Hyper Operator Overlayarchitecture;

[0025]FIG. 2 schematically shows an embodiment of a hierarchical accessnetwork environment that is integrated with a Hyper Operator inaccordance with the present invention;

[0026]FIGS. 3a-b schematically show various binding update messagedifferences between handoff and non-handoff in terms of the care ofaddress change for the hierarchal access network environment of FIG. 2;

[0027]FIG. 4 schematically shows transmission of a binding updatemessage for the hierarchal network environment of FIG. 2 and handoffdecision based on an access network topology information in accordancewith the present invention;

[0028]FIG. 5 schematically shows a second embodiment of a hierarchicalaccess network environment that is integrated with a Hyper Operator thatillustrates a physical access network topology map constructed inaccordance with the present invention;

[0029]FIG. 6 schematically shows an embodiment of a registration requestpacket (Mobile IP binding update message) that can be sent to the homeagents (Hyper Operators) of FIGS. 2 and 5 in accordance with the presentinvention;

[0030]FIG. 7 schematically shows a third embodiment of a hierarchicalaccess network environment that is integrated with a Hyper Operator inaccordance with the present invention;

[0031]FIG. 8 schematically illustrates an embodiment of a physicalaccess network topology map constructed for the hierarchal accessnetwork in accordance with the present invention;

[0032]FIG. 9 schematically shows a possible frequency distribution ofhandoff occurrence between the hierarchal access network of FIG. 7;

[0033]FIG. 10 shows a flow chart of an embodiment of sending a bindingupdate message with a time stamp in accordance with the presentinvention; and

[0034]FIG. 11 schematically shows another embodiment of a physicalaccess network topology map based on the directional consideration to beused with the hierarchal access networks in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] In accordance with the present invention the heterogeneity ofdifferent access networks is mitigated by coordinating and organizingheterogeneous access networks. As for the coordination, it is importantto exchange necessary information between heterogeneous access networks.In order to facilitate the exchange of information, a physical accessnetwork topology is built at the Hyper Operator which will automaticallycollect, analyze, and track the geographical access networkconfiguration, even though each access network operator does not providephysical topology information to the Hyper Operator. Building such atopology is desired since each access network operator may not or cannot provide details of access network topology information such as thebase station location and the coverage area. Therefore, it is desired tobuild a network topology that will allow the Hyper Operator toautomatically track the physical access network topologies inheterogeneous access networks. It is noted that the physical accessnetwork topology map described above represents the geographicalrelationship among Internet provider subnets of different accessnetworks or 'same access network.

[0036] During construction of the physical access network topologydescribed above, a number of factors preferably should be addressed,such as:

[0037] 1) How is the physical access network topology determined withoutidentifying and interrogating each access network operator?

[0038] 2) How to update the physical access network topology map?

[0039] 3) How to improve the accuracy of the physical access network mapin view of the fact that the Hyper Operator must estimate thegeographical access network configuration? and

[0040] 4) How is the constructed physical access network topology map tobe used in order to improve the mobile device and network performancesin terms of vertical handoff, network selection, power consumption etc.?

[0041] Taking into account the above factors, the construction of aphysical network topology network map is understood by first reviewing atypical hierarchical access network environment that is integrated witha Hyper Operator as shown in FIG. 2.

[0042] The access network environment 200 includes a variety of accessnetworks 202A-E, 204A-F, 206A-B that have small, medium and largecoverage areas, respectively. As shown in FIG. 2, the access networks202A-E are in communication with access routers (AR) AR5-7, which canwork as a foreign agent of Mobile IP, access networks 204A-F are incommunication with access routers AR3-AR4 and access networks 206A-B arein communication with access routers AR1-AR2. Each access router AR1-7is in communication with the Hyper Operator or home agent 208.

[0043] As described in Hyper Operator Overlay architecture, the layer 3has a commonality to use IP in each access network. In the architectureof FIG. 2, Mobile IP, such as described in C. Perkins, “IP mobilitysupport,” IETF RFC2002, Oct. 1996, is implemented in each access networkfor the IP mobility. In Mobile IP, the mobile device, such as a cellphone, PDA or a lap top computer 210, sends a binding update message(BU) to the home agent 208 whenever a new care of address (CoA) isobtained from one of the access routers AR1-7. In particular, FIG. 5shows that the mobile device 210 handoffs from AR3 to AR1, from AR1 toAR2, and from AR2 to AR4. At each handoff, a binding update message istransmitted to the home agent 208. When the home agent 208 accepts thebinding update message, the home agent 208 begins to associate the homeaddress of the mobile device with a new care of address and maintainthis association until the registration lifetime, the time that bindsthe home address (permanent IP address) and the care of address(temporary IP address), expires. In this embodiment the mobile devicehas the home address assigned by the Hyper Operator.

[0044] The geographical access network configuration of FIG. 2 overservice areas of different access network providers is estimated byusing the binding update messages in Mobile IP. Because of the care ofaddress (CoA) change in case of the handoff, the receiving of a newbinding update message indicates a geographical overlapping between aprevious associated subnet and a new subnet. When the Hyper Operator(works as a home agent) tracks the binding update message, the physicalaccess network topology map representing IP subnets relation can bebuilt at the Hyper Operator. According to this map, the user is aware ofcurrent neighboring access networks after the user downloads thephysical access network topology map or gets information from the HyperOperator through a current associated network. Note that constructingthe physical access network topology map based on the binding updatemessage according to the present invention provides for mobilitymanagement, appropriate access network selection and energy efficiency.

[0045] Sending the binding update message explicitly indicates that themobile device obtains different care of address from the new accessrouter, however, this binding update message does not indicate whetherthe care of address change has occurred by the handoff or not. If thebinding update message is originally triggered by the handoff, thereceiving binding update message implicitly indicates the physicalcoverage overlapping between the current access router and the targetaccess router. This is because the handoff occurs only when both the oldaccess router and the new access router are overlapping.

[0046] However, one problem with building the physical access networktopology map on the binding update messages is that the transmission ofa binding update message occurs even if the mobile device is turned-offat one cell and after the mobile device moves to another cell it isturned-on. The trigger difference between handoff and non-handoff interms of care of address change is illustrated in FIGS. 3(a)-(b). Forexample, FIG. 3(a) indicates the mobile device handoff, while FIG. 3(b)shows when the mobile device is turn-off and the mobile device moves toanother cell before it is turned-on. Both cases cause the care ofaddress to change. Differentiation between the situations illustrated inFIGS. 3(a)-(b) is important to create the access network topology mapaccurately. This is especially seen in the situation where the mobiledevice 210 is turned off in one city and then moved to another city.When the mobile device 210 is turned on in the other city, the bindingupdate message is sent to the home agent 208. Consequently, the homeagent 208 will misunderstand that the previous access router and the newaccess router are closer each other, even though these two accessrouters are located in different places.

[0047] One solution for this distinction, according to the presentinvention, is that the binding update message is transmitted through theold access router to the home agent 208 when the mobile device obtainsthe new care of address, instead of from the new access router to thehome agent 208 as done in the past with Mobile IP, as shown in FIG. 4.Examples of such transmission are shown in FIGS. 2 and 5. For instance,in FIG. 2 the binding update message is transmitted from AR4 (old accessrouter) instead of AR2 (new access router). In another example shown inFIG. 5, the binding update message is transmitted from AR3 instead ofAR1. In each of the examples of FIGS. 2 and 5, the care of addresschange between the old access router and the new access router may notindicate the geographical proximity. By tracking care of address changeto establish the access network topology map, it is necessary to knowwhich access networks are geographically overlapping. The reason totransmit the binding update message via the old access router is todistinguish the handoff or not for the current care of address change.If the mobile device 210 is able to associate with the new access routerand sends a binding update message through the old access router, thisindicates that the mobile device 210 is located in the overlapping areabetween the old and new access routers. This scheme requires only aslight modification in Mobile IP. The difference is that the originalMobile IP uses the new access router to send the binding update message.The use of the old access router to send the binding update messageincreases the accuracy of the geographical network topology mapdetermined in accordance with the present invention.

[0048] After the home agent 208 receives the binding update message, thehome agent 208 will update a packet forwarding table which associatesthe home address of the mobile device 210 with the new care of addressbased on the binding update message, and at the same time, the homeagent 208 constructs an IP relation map between the new care of addressand the old care of address.

[0049] An advantage of the above mentioned architecture is that even ifthe home agent 208 cannot obtain the user's location information andaccess network topology from each access network, the binding updatemessage is always received at the home agent 208 as long as each accessnetwork deploys Mobile IP. It is assumed that the access router controlsonly access points that belong to single access network. Hence, eventhough the hierarchical mobility management scheme described in A. T.Campbell et al., “Design, implementation and evaluation of cellular IP,”IEEE Pers. Commun., vol.7, no.4, pp.42-49, Aug. 2000 and A. T. Campbellet al., “Comparison of IP micromobility protocols,” IEEE WirelessCommun., vol.9, no.1, pp.72-82, Feb. 2002, is used, the binding updatemessage will be received at the home agent 208 whenever the associatedcare of address is changed.

[0050] As the home agent 208 receives many binding update messages fromdifferent mobile devices, the home agent 208 can build the IP relationmap between access networks in the whole service coverage area. Sincethe different access network has a different IP subnet, IP relation canbe considered as an access network relation as well. An example is shownin FIG. 5. The home agent 208 will be distributed over Internet in thearchitecture, which we call the Hyper Operator Overlay node (114A-C).The Hyper Operator Overlay node has the same functions as the HyperOperator. In order to have a scalability, the Hyper Operator Overlaynode should work as the Hyper Operator. An access router is composed ofIP subnet and some access points. Whenever the care of address ischanged, the mobile device 210 will send the binding update message tothe home agent 208.

[0051] According to another embodiment of the present invention, L2 orabove L4 information is included into a part of an extension in thebinding update message.

[0052] Since the care of address changes do not indicate the handoff, L2level or above L4 information included in the binding update message,which explicitly indicates handoff, helps to distinguish the handoffoccurrence. FIG. 6 shows the Registration Request packet (the bindingupdate message) that is sent to the home agent 208 and is defined in C.Perkins, “IP mobility support,” IETF RFC2002, Oct. 1996. An extensionpart of this packet can include L2 level and above L4 information. Forinstance, as L2 level information, the associated access point MACaddress is changed. As for the case when L4 level information isincluded in the binding update message, such information as whether thedevice is a mobile device or not, and how fast it can move, etc. isincluded.

[0053] As the binding update message based on the handoff is collectedat the home agent 208, IP relation in terms of physical overlapping willbe built. As mentioned earlier, different access networks have differentIP subnets so that IP relation can be considered to be equivalent to anaccess network relation. Consequently, the physical access networktopology map (access network are physically neighborhood) can be createdafter some mobile devices handoff between different access networks. Themore the handoff occurs among different access networks, the moreaccurate the relationship between access routers in the physical accessnetwork topology map can be affirmed. In FIG. 5, an example of an accessnetwork topology map 212 constructed as the result of mobile device 210moving from AR3 to AR1 to AR2 and AR4 is shown at the home agent 208.

[0054] To increase further accuracy of the physical access networktopology map, the home agent 208 will track the direction of thehandoff. As shown in FIG. 7, the mobile device 210 handoffs from AR3 toAR1, then this map guarantees the physical overlapping and neighboringfrom AR3 to AR1. However, the binding update message generated by ahandoff from AR3 to AR1 will not fulfill a bi-directional handoffbetween AR3 and AR1 (see FIG. 8). A couple of reasons are: the mobiledevice 210 located in AR1 (larger cell size) may not be able to handoffto AR3 (smaller cell size) based on the only proximity informationbetween AR1 and AR3. Another case is that the propagation condition isdifferent at a different path. Therefore, the mobile device 210 may notbe able to handoff in a mutual way. An important point is that this mapmay not significantly improve the downward handoff from the larger cellto the smaller cell, since the upward vertical handoff from the smallercell to the larger cell has a serious time critical problem described inM. Stemm and R. H. Katz, “Vertical handoffs in wireless overlaynetworks,” Mobile Networks and Applications, vol.3, no.3, pp.335-350,1998. Therefore, this map is still effective to reduce the handoff time,which is needed for the handoff from the smaller cell to the largercell.

[0055] Another embodiment of the present invention where themodification of the Mobile IP is minimized makes use of the frequency ofthe movements between one subnet and another subnet. Based on the numberof the care of address changes between one access network and anotheraccess network, access network topology relation will be solid. Thismethod does not need to distinguish handoff which will trigger thebinding update message transmission. For instance, the home agent 208may receive several binding update messages from AR3 to AR1 and onebinding update message from AR3 to AR4. In this example, the HyperOperator can affirm the overlapping between AR1 and AR3, but the onebetween AR3 and AR4 cannot be confirmed because of the low handofffrequency between the two. Another example is shown in FIG. 9. In thisexample, the number beside the arrow indicates how many time the bindingupdate messages change between access routers. Based on this number, thegeographical relationship between the access routers will be taken intoaccount. If the number is large, the probability of handoff chancebetween the access routers is high. For instance, the mobile device 210most probably can handoff from AR3 to AR1, but this map will notguarantee the handoff from AR1 to AR3. Thus, based on the frequency ofhandoff experiences between access routers stored in the Hyper Operator,it can be determined whether or not the mobile device 210 can handoffbetween particular access routers. This knowledge increases the accuracyof the geographical network topology map determined in accordance withthe present invention.

[0056] Another embodiment of the present invention where themodification of the Mobile IP is minimized is shown by the flow chart300 of FIG. 10 where a time stamp is established in the binding updatemessage of Mobile IP, the time stamp is based on the time of receipt ofthe binding update message. The time stamp is included in the extensionof the registration request shown in FIG. 6. The time stamp is used forthe case where the mobile device 210 loses connection with one accessrouter and later gains connection with another access router. As shownin FIG. 10, the home agent 208 determines if the mobile device 210 haslost connection with an access router per step 302. Upon detecting alost connection with an access router, a lost time stamp is establishedin the database per step 304.

[0057] While the home agent 208 determines if connection with a mobiledevice 210 is lost, the home agent 208 monitors the receipt of bindingupdate messages from the access routers of the network per step 306since such receipt indicates that a change in access router hasoccurred. Since the mobile device 210 may have different IP addresses(multiple IP address assignment) for each access network interface(depending on the implementation), therefore the home agent 208 has toidentify whether the device associated with the lost connection of step302 is the one that sends the binding update message of step 306. Thisis accomplished by first having the home agent 208 check the homeaddress of the mobile device per step 308. If the home addresses for themobile devices associated with the lost connection and the bindingupdate message are the same, the binding update message is deemed tohave originated from the same device per step 310. If the home addressesdo not agree, then the identification numbers of the devices are checkedper step 312. If the identification numbers do not correspond to oneanother per step 314, then the home agent 208 will identify the mobiledevice associated with the binding update message as a new device andwill register the new device at a table within the home agent 208 perstep 316.

[0058] Should the devices be deemed the same at either step 310 or 314,then the home agent 208 will check the time stamp which is included inthe binding update message per step 318. As shown in step 322, the homeagent 208 will compare the current time stamp with the lost connectiontime stamp, retrieved per step 320 which was stored in the home agent'sdatabase. If the difference of the time exceeds the threshold, such asthe maximum time of IP address change, then the home agent 208 willconsider that this binding update message is not triggered by thehandoff per step 324 and so determine that there is no geographicalrelationship between the access routers corresponding to the lostconnection and the binding update message. For example, suppose themobile device 210 is turned off, then the user transports the samemobile device 210 to another location. After movement, the mobile deviceis switched on. In this case, the lost connection time is large enough.So, the home agent 208 can recognize that the binding update message isnot originated by the handoff.

[0059] On the other hand, if the difference of the time does not exceedthe threshold, then the home agent 208 will consider that this bindingupdate message is triggered by the handoff per step 326 and that ageographical relation is assumed to be established between the accessrouters in terms of a function of the difference of the time. Based onthe above observation, the physical access network topology map will beupdated. This means that the relation between the previous access routerand the new access router is mapped in the physical access networktopology map as shown in FIG. 11. It is noted that “threshold” will bedecided based on the implementation. If the threshold is short, theaccuracy of the physical access network topology map is increased butthere is a time stamp synchronization problem to be considered. If thesynchronization difference time between the mobile device 210 and thehome agent 208 is large, it may happen that the value of current timestamp minus connection lost time stamp will be a negative value.Therefore, the map will be inaccurate.

[0060] After the Hyper Operator has the access network topology map perthe various schemes described previously with respect to FIGS. 2-10, themap can leverage seamless experience for the user. It is assumed thatthe Hyper Operator has the physical access network topology map as shownin FIG. 11. First of all, the Hyper Operator can identify the mobiledevice location in terms of IP subnet level based on the current care ofaddress. In the example shown in FIG. 11, the mobile device 210 iscurrently located in the AR5. As the Hyper Operator has topologyinformation, it shows what access networks are available around thecurrent user's location, which access networks are appropriate for thecurrent application, which access networks are preferable etc. Based onthis map, the Hyper Operator identifies the physical relation of otherARs related to the AR5, so that the Hyper Operator can suggest themobile device which access network interface should be activate.Consequently, the mobile device 210 can save the battery drain becauseit can turn off unavailable access network interfaces. In this example,the mobile device 210 at AR5 should only turn on the access networkinterface for AR2 and AR4. Current access network selection in theheterogeneous access network has been studied based on the range,capacity, and delay as described in J. Kaliokulju et al., “Radio accessselection for 10 multistandard terminals,” IEEE Commun. Mag., vol.39,no.10, pp.116-124, Oct. 2001.

[0061] Mainly the market aspect is omitted. However, the Hyper Operatorcan assist the mobile device; what networks are available around thecurrent user's location, cost of usage based on the user's preference,maximum available bandwidth, and level of security. For example, theHyper Operator can identify a paging area based on the neighboringaccess routers around a current access router by using the physicalaccess network topology map.

[0062] The foregoing description is provided to illustrate theinvention, and is not to be construed as a limitation. Numerousadditions, substitutions and other changes can be made to the inventionwithout departing from its scope as set forth in the appended claims.

We claim:
 1. A method of coordinating the handoff of a mobile carrierbetween a first access network and a second access network, the methodcomprising: handing off from a first access network that said mobilecarrier is currently operating within to a second access network; andbuilding a physical access network topology based on said handing offwithout input from either said first access network or said secondaccess network.
 2. The method of claim 1, wherein said building isaccomplished without identifying or interrogating operators of eithersaid first access network or said second access network.
 3. The methodof claim 1, wherein said first access network communicates with a firstaccess router and said second access network communicates with a secondaccess router.
 4. The method of claim 3, wherein said first accessrouter and said second access router communicates with a home agent. 5.The method of claim 4, wherein said home agent comprises a HyperOperator and Hyper Operator Overlay Node.
 6. The method of claim 1,wherein a size of a coverage area of said first access network differsfrom a size of a coverage area of said second access network.
 7. Themethod of claim 1, wherein Mobile IP is implemented in said first accessnetwork and said second access network.
 8. The method of claim 4,further comprising sending a binding update message from one of saidfirst and second access routers to said home agent.
 9. The method ofclaim 8, wherein said first access router sends said binding updatemessage to said home agent.
 10. The method of claim 1, wherein saidbuilding is accomplished with a binding update message which includes aforeign agent address.
 11. The method of claim 9, wherein said sendingoccurs when a new care of address message is received from said secondaccess router.
 12. The method of claim 8, wherein said building aphysical access network topology comprises estimating said physicalaccess network topology based on said binding update message.
 13. Themethod of claim 12, wherein said binding update message indicates ageographical overlapping between said first access network and saidsecond access network.
 14. The method of claim 1, further comprisingdetermining whether said mobile device has been turned off from the timesaid mobile device was present within said first access network to whensaid mobile device is present within said second access network.
 15. Themethod of claim 12, further comprising determining whether said mobiledevice has been turned off from the time said mobile device was presentwithin said first access network to when said mobile device is presentwithin said second access network.
 16. The method of claim 8, whereinsaid binding update message comprises an extension that containsinformation that distinguishes a handoff occurrence.
 17. The method ofclaim 16, wherein said information is L2 level information.
 18. Themethod of claim 16, wherein said information is above L4 levelinformation.
 19. The method of claim 16, wherein said binding updatemessage comprises an extension that contains information that determineswhether there is a geographical relation between said first accessrouter and said second access outer when said mobile device has lostconnection with both said first access router and said second accessrouter.
 20. The method of claim 19, wherein said information is a timestamp indicating when said mobile device lost connection.
 21. The methodof claim 1, further comprising tracking a direction of said handoff. 22.The method of claim 7, further comprising tracking a number of care ofaddress changes between said first access network and said second accessnetwork.
 23. The method of claim 22, further comprising determiningwhether there is overlapping between said first access router and saidsecond access router based on said number of care of address changes.24. The method of claim 1, further comprising suggesting an accessnetwork interface to be activated by said mobile device based on saidphysical access network topology.
 25. The method of claim 1, furthercomprising identifying a paging area based on the neighboring accessrouters around the current associated access router by using saidphysical access network topology map.
 26. The method of claim 1, furthercomprising identifying an access network interface to said mobile devicethat is unavailable to said mobile device.
 27. The method of claim 24,further comprising identifying an access network interface to saidmobile device that is unavailable to said mobile device.
 28. A method ofdetermining a geographical relationship between a first access networkand a second access network as a mobile device moves between a firstaccess network and a second access network, the method comprising:losing connection with a mobile device located within a first accessnetwork; establishing connection with said mobile device within a secondaccess network; and determining a geographical relationship between saidfirst access network and said second access network based on achronological relationship between a time of said losing connection anda time of said establishing connection.
 29. The method of claim 28,wherein said determining is performed without input from either saidfirst access network or said second access network.
 30. The method ofclaim 28, wherein said determining is accomplished without identifyingor interrogating operators of either said first access network or saidsecond access network.
 31. The method of claim 28, wherein said firstaccess network communicates with a first access router and said secondaccess network communicates with a second access router.
 32. The methodof claim 28, further comprising: establishing a first time stamp basedon a time of occurrence of said loss of connection; establishing asecond time stamp based on a time of receiving of said binding updatemessage and wherein said determining is based on said first time stampand said second time stamp.
 33. The method of claim 32, wherein saiddetermining is based on a difference between said first time stamp andsaid second time stamp.
 34. The method of claim 28, further comprisingdetermining whether said mobile device associated with said losingconnection is the same as a mobile device associated with saidestablishing connection.
 35. The method of claim 34, further determiningwhether said mobile device with said sending binding update message isthe same as a mobile device associated with said losing connection basedon the device identity.
 36. The method of claim 34, wherein saiddetermining is performed even if a home address of said mobile deviceassociated with said losing connection is different than a home addressof said mobile device associated with said establishing connection. 37.The method of claim 28, further determining whether said mobile devicecan handoff from a first access router to a second access router basedon a frequency of handoff experience between said first access routerand said second access router.
 38. The method of claim 37, wherein theaccuracy of said geographical relationship between said first accessnetwork and said second access network is increased based on thefrequency of handoff between said first access router and said secondaccess router.
 39. The method of claim 28, further comprising handingoff from a first access router to a second access router, wherein theaccuracy of said geographical relationship between said first accessnetwork and said second access network is increased based ontransmitting a binding update message through said first access routerinstead of transmitting through said second access router.